This invention relates generally to afterburners or augmentors, and, more particularly to a turbofan augmentor flameholder for use in a turbofan engine.
It is well known in the aircraft gas turbine art to provide thrust augmentation by burning additional fuel in an afterburner or augmentor located downstream of the engine turbine. The afterburner generally includes means for dispersing a main flow of fuel together with a flameholder to which the flame may attach. The flameholder reduce locally the velocity of the gas stream in order to sustain the flame which would otherwise blow out. Generally, the flameholder is made up of an annular pilot burner located near the outside of the hot core of the turbine engine with radial vee-gutter flameholders extending into the hot core and the cool fan duct air of the turbofan afterburner. For typical vee-gutter flameholder, the limit of flame stability is controlled by the combustion rate in the recirculation zone behind the gutter. At high altitude, the inlet pressure and temperature are reduced which results in a poor combustion rate and, thus, poor flame stability limits. It is well known that by introducing a source of heat to the recirculation zones, the reaction rate and stability limits may be increased. Unfortunately, attempts to introduce this heat source by gas migration from the adjacent hot core have resulted in either durability problems or design constraints.
Several other methods and their associated problems are listed hereinbelow:
1. The inclined flameholder: By moving the outer diameter fan duct gutter tips aft, a forced migration is directed from the core section or pilot section into the fan duct gutter wakes. Unfortunately, this method of migration produces excessive thermal loads on the walls of the augmentor downstream of the flameholder.
Forced flow via scoops: Scoops located on the pilot zone may be used to force hot flow down the fan duct radial gutters. The problems are mechanical and thermal durability of the scoops, which are located in the hot recirculation zone, are affected thereby. A secondary problem is disruption of the recirculation zone aerodynamics. As a result, the forced flow via scoops generally has not been utilized in practical applications.
It is therefore quite obvious that the current state-of-the-art turbofan augmentor flameholders leave much to be desired in that poor flame stabilization occurs in the low temperature fan duct air stream. In addition, the durability of the liner has been reduced as a result of the introduction of an additional heat source to the recirculation zone.